Telephonic call magneto



A. DUCRUET TELEPHONIC CALL MAGNETO Nov. 7, 1950 3 Sheets-Sheet 1 Filed May 2, 1950 Anonmsyg A. DUCRUET TELEPHONIC CALL MAGNETO Nov. 7, 1950 a Sheets-Sheet 2 Filed May 2, 1950 nun HIM INVEN70R' ,9/27f/0R buoRuET wmmm mi, M,

'Nov. 7, 1950 A. DUCRUET TELEPHONIC CALL MAGNETO 3 Sheets-Sheet 3 Filed May 2, 1950 INVENYoR; IQRTHUR mac/Rue?- 3, LI /um, Amd/ P Patented Nov. 7, 1950 I 2,528,874 TELEPHONIO CALL MAGNETO Arthur Ducruet, Paris, France Application May 2, 1950, Serial No. 159,621 In France October 13, 1943 1 Claim.

This application is a continuation-in-part of application Serial No. 631,391 filed November 28, 1945.

My invention relates to a telephonic call magneto of the unwound rotor type.

One important object of my invention is to provide a magneto of the unwound rotor type which will be at least not larger than the usual dialing plate of automatic telephone apparatuses, and will fit within the same space as that occupied by such a dialing plate, i. e. in a cylindrical space about 80 mm. in diameter and 35 mm. high.

A telephonic call magneto designed for the same purpose has been described in application Serial Number 639,087, filed Jan. 4, 1946. by Charles Laurent, patented Nov. 22, 1949, No. 2,488,821. Owing to the fact that the axle of the prior art magnetos is offset relative to the rotor shaft, and that, owing to this arrangement, the total space occupied by these magnetos is much larger, the magnetos of this latter type are driven by a toothed rack situated in a plane parallel to the rotor magnet. This arrangement is, however, detrimental when the magneto designed to occupy the place of the call dial, instead of emerging from the casing of the tele phonic apparatus, is inserted in one of the faces of this casing. It then becomes necessary to extend the toothed rack up to the side perpendicular to the face into which the magneto is inserted, and closest to the insertion socket, so as to render the rack accessible, and this extension may lead to a great length. I

Moreover, in the magneto referred to hereabove, the permanent magnet rotor rotates in front of the stator, and not inside of the stator, which increases the height of the cylindrical volume into which the telephonic call magneto must be confined.

Another object of my invention is to provide a magneto which might be inserted in the casing wall of a telephonic apparatus, and the driving means of which, of a toothed-rack and free wheel type, provided on the magnetos 'upper face, would be entirely comprised within the cylindrical space the size of which has been previously defined.

The new device is characterized by the provision of a novel kind of driving means for the magnet rotor, a novel kind of switch actuating means, a novel, very fiat cylindrical form of the magnet, and a torus shaped stationary tromotive force, in spite of the small volume of the magneto.

My invention will, however, be best understood from the following description with reference to the accompanying drawings, whereas those features of my invention which are believed to be novel and lpatentable are pointed out in the appended claim.

Figure 1 is a plan view of the novel magneto viewed from above, the upper lid being removed;

Figure 2 is the corresponding side view;

Figure 3 is a plan view of the magnetos magnet and windings viewed from above;

Figure 4 is a cross section along the line :r-O-g of Figure 3;

Figures 5a, 5b and 5c illustrate the three parts forming the magnetos casing.

As shown in the drawings, my improved magneto comprises a fiat cylindrical rptary magnet I of material having the desired magnetic characteristics, such as Alnico, so magnetized as to be provided with two pairs of poles denoted by N and S, with their magnetic axes perpendicular to each other, and a stationary armature 2 consisting of one-piece annular laminae 3 superposed to form a toroidal square section structure.

In four sectors 1 the cross-section of the stator armature is reduced to about a half of its normal section, to form the cores of the windings. Each of these sectors has an angular development substantially equal to the interval between the two successive sections, 1. e. each core I has substantially the same length as each polar piece 46 of the inductor. Four generating coils 5 are fitted in the slots 8 provided on the inner side of the structure and extending in parallel to the shaft 4 of the rotor; one

. of these coils is not represented. The side wall armature, said driving means, switch actuating 6 of the slots extend in radial planes, and so do the individual windings of the coils. Being wound around the reduced section I of the annular armature, the inner parts of the coil windings are completely hidden in the slots and do not project beyond the inner'periphery of the armature, whilst approaching the circumferential surface of the cylindrical rotor l 0s closely as to leave only a gap wide enough to prevent frictional contact with its surface.

The four coils are connected in series by connections such as 48, so that the instantaneous electromotive forces developed in each of the coils are added one to another.

29 are the bores drilled in the laminae and designed for assembling the laminae by means of rivets 47. 24 are the bores for assemblage of the inductor'in the casing, and 23 are the cuttings used for centering of the inductor inside of the casing, as will be seen later on.

The magneto casing manufactured preferably in a light metal such as aluminium comprises three parts 9, II] and H.

The lower part 9 has a cylindrical shape 0.8 cm. high and 8 cm. diameter, and its bottom is partially hollowed by two holes l2 and E3 to reduce the weight. The cylinder is provided with two notches I4 and I5, and with a central bore ll for the passage of the rotors shaft 4; two bores [6 give passage to the assemblage screwsof the cas- The median part IE] has a cylindrical shape of some 1.2 cm. high, and it fits into the former part; its upper portion is closed by a front flange IE; it is provided with partial notches l9 and of the same profile as the notches l4 and 15, with a central bore 2! for the passage of the shaft 4 of the rotor, and with two bores 22 for passage of the assemblage screws of the casing,

The notches i4, l5, l9 and 20 which correspond to the bossings inside of the casing cooperate for centering of the inductor the core of which is provided with cuttings 23 having the same shape asthe bossings. When the inductor is placed in a proper position inside of the casing the screw bores l6 and 22 fall in front of the screw bores 2 idrilled in the inductors core, and the assemblage is then made by means of bolts and nuts.

On the other hand, the bores 25 drilled in the part It] serve to give passage to the screws for fastening of the magneto to the telephonic apparatus. i v

The upper part i l of the casing is a lid stamped out of aluminium plate. This lid is fastened to the assemblage by means of props 26 engaged in a circular groove 21 provided on the part ii] of the casing. This lid I l is provided with a bore 28 leaving passage to the axle of the driving lever 38.

The adjustment of the magnets reluctance in conformity with that of the gap is obtained by designing the magnet and the gap, as far as their proportions are concerned, in such a manner that the point in which the magnet passes through the position of stable equilibrium with respect to the armature, i. e. in position of maximum'fiux, is located in the part of the hysteresis cycle which corresponds to the maximum product B H of the material used for the magnet. The variation of the energy during the rotation of the magnet is thus a maximum. 7

An association of a normal gap of 2 to 3 tenths of a millimeter with an alloy such as Alnico, with the size and number ofpoles (four poles) given to this magnet, and with the size of the magneto structure itself allows me to obtain this result whilst satisfying the requirements as to the space taken up by this arrangement.

As to the adjustment of the internal impedance of the magneto, the impedance of the loading circuit constituted 'by the call circuit at the frequencies provided by the magneto may be lower than 600 ohms, and be even as low as 300 ohms in certain cases. In order to be capable, in such cases, to adjust the impedance of the generator in conformity with that of the circuit, I have resorted, according to my invention, to the following arrangements:

The mean coil of the armature is made as short as possible, so as to reduce the ohmic resistance to a minimum.

The magnetic circuit has a small cross section 2,528,874 if T in the portions 1, in order to reduce the imaginary part of the internal impedance by way of saturation of the poles.

These arrangements together with the small size of the whole device result in a magneto of restricted Volume in which the ratio between the electromotive force and the difference in voltage at the terminals of a resistance of 600 ohms is only 1.25, instead of 2.5 'or 3 as in the conventional type of magnetos. The novel one allows an optimum adjustment for 300 ohms.

These results are due to the fact that the ring is the geometrical figure which makes use of the whole volume of the annular space left between the cylindrical magnet and the outer diameter of the magneto, depending on the shape of the dial,

whereas any other geometrical figure would leave a portion of said space unutilized.

On the other hand, the winding of the coils around the annular armature produces the shortest possible coils which offer the minimum of resistance.

In this way the space available is used to a maximum, and on the other hand, the leakage flux is very much reduced, and the inductance is small, whilst the internal impedance of the magneto is reduced to a minimum.

Without modifying the telephonic apparatus, and without adding any complementary part, I thus ensure, owing to the shape of the armature, the possibility of interchanging the magneto and the dial.

The driving lever 30 is rigid with the toothed sector 3!, and it enables to drive the magnetos rotor by means of a free wheel device.

The toothed sector is pivotable about a spindle 32 carried by the front flange iii of the cylinder I0, and the return of the toothed sector into its operative position is ensured through a spring 33 arranged round the spindle 32 carrying the sector and abutted against the pin 34.

As the counter-magnetomotive force of the magneto is high, and since it is not feasible to reckon upon a great number of revolutions performed through the free wheel device, it is necessary that the operation of the lever 30 actuates the rotor on the greatest possible number of revolutions, in order to collect the greatest pos sible force at the terminals of the magneto.

In view of this the spindle 32 is located at the outer rim of the front flange l8, and under these circumstances the toothed sector 3! which intermeshes with the pinion 35 centered on O has a radius substantially equal to that of the cylindrical volume occupied by the magneto and has an angular development of about The pinion 35 has the smallest diameter compatible with the mechanical conditions, and in taking a pinion of 7 mm. of diameter and 16 teeth, anda sector of 38 mm. diameter and 32 teeth, it is possible to drive the rotor through two entire revolutions by actuating the levertfl from its extreme left to its extreme right position. As, under these conditions of operation, both extreme left and extreme right positions of the lever, correspond to the two equilibrium positions of the magnet, and in which the poles of the rotor aresituated in front of the polar pieces of the stator 2, and which are also the maximum driving torque positions, it is possible, in ending the driving stroke of thelever 30 with a sufiicient finger pressure to obtain a rotation of the rotor for at least one quarter revolution in free wheel run, corresponding to the interval between the equilibrium position occupied at the end of its stroke, and,

the equilibrium position immediately succeeding the same.

In order to avoid that the end of the lever would project out of the cylindrical profile confining the magneto in the two extreme positions of the lever at the end of its 60 stroke, the length of this lever must not exceed:

x40 mm.

which is the side of an equilateral triangle inscribed in a circle of 80 mm. diameter.

The pinion is rigid with a flat disc 35 bearing a ratchet 39 loaded by a spring 37 and intermeshing with a pawl pinion 38 keyed on the axle V 4 of the magnet The whole arrangement forms a free wheel device which drives the magnet only when the lever 30 is pushed in one direction from the left to the right.

The conventional switching device which allows the difference between the calling and the inoperative position of the magneto to appear is provided by three superposed spring blades '40, 4| and 42 placed under the left portion of the toothed sector in its idle position.

In the inoperative position, the blades and 4| are maintained in touch by abutment against a pin 43 borne by the toothed sector through a pusher 44 rigid with the blade 4| and passing through a bore provided in the blade 42. The blade 40 is pushed to the left, and its displacement is restricted by an abutment 45 made of an insulating material.

In the calling position, on the contrary, the blades 4| and 42 are maintained in touch.

It is thought that the invention and its advantages will be understood from the foregoing description and it is apparent that various changes may be made in the form, construction and arrangement of the parts Without departing from the spirit and scope of the invention or sacrificing its material advantages, the form hereinbefore described and illustrated in the drawings being merely a preferred embodiment thereof.

Iclaim:

In a telephonic call magneto designed to be interchangeable with a telephonic calling dial, in combination, a, magnetic rotor having a flat cylindrical shape magnetized for north poles in two opposite quadrants, and for south poles in the two opposite quadrants adjacent to the former ones, and rotatable from one of four rest positions to another of these positions, a stator of a toroidal shape formed by superposition of annular 1aminae cut out in four places by notches the sides of which are situated in radial planes of the torus, the angular development of each notch being the same as that of the polar pieces located between each two notches, generating coils wound on said notches, intermittently driving means of the rotor comprising a lever, a toothed sector having a radius but slightly smaller than that of the magneto itself and an angular development of about and a free Wheel device designed to supply at least two full revolutions of the rotor for one 60 stroke of the driving lever, said driving means having rest positions in which the rotor poles face exactly the stator polar pieces, and simultaneously serving for actuating, in their rest positions, the connection contacts.

ARTHUR. DUCRUET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Num er Name Date 685,685 Krahenbuhl Oct. 29, 1901 697,963 Apple Apr. 22, 1902 877,284 Berglund Jan. 21, 1908 942,325 Huber Dec. 7, 1909 1,947,269 Leibing Feb. 13, 1934 2,071,536 Kalin Feb. 13, 1937 2,131,436 Howell Sept. 27, 1938 2,193,675 Merrill Mar. 12, 1940 2,390,877 Fisher Dec. 11, 1945 FOREIGN PATENTS Number Country Date 271,592 Great Britain June 2, 1927 

